U.S. patent application number 12/231920 was filed with the patent office on 2009-03-19 for rechargeable battery assembly and power system using same.
Invention is credited to Chun-Chieh Chang, Tsun-Yu Chang, Olivia Pei-Hua Lee.
Application Number | 20090072793 12/231920 |
Document ID | / |
Family ID | 40453759 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090072793 |
Kind Code |
A1 |
Chang; Chun-Chieh ; et
al. |
March 19, 2009 |
Rechargeable battery assembly and power system using same
Abstract
A rechargeable battery, battery set or battery pack having a
circuit or a plurality of circuits for providing self-discharging
thereof electrically connected in parallel are used to form
rechargeable battery assemblies and electric power supply systems
for use in electric and hybrid vehicles and the like.
Inventors: |
Chang; Chun-Chieh; (Ithaca,
NY) ; Chang; Tsun-Yu; (Taichung, TW) ; Lee;
Olivia Pei-Hua; (Fort Lee, NJ) |
Correspondence
Address: |
KRATZ, QUINTOS & HANSON, LLP
Greater Beneficial Union of Pittsburgh Building, 4232 Brownsville Road
Suite308
Pittsburgh
PA
15227
US
|
Family ID: |
40453759 |
Appl. No.: |
12/231920 |
Filed: |
September 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11805786 |
May 24, 2007 |
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12231920 |
|
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60923747 |
Apr 17, 2007 |
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Current U.S.
Class: |
320/134 |
Current CPC
Class: |
H01M 10/441 20130101;
B60L 53/00 20190201; H02J 7/0016 20130101; B60W 20/00 20130101;
Y02T 10/70 20130101; B60W 10/26 20130101; B60L 2200/12 20130101;
Y02E 60/10 20130101; Y02T 10/7072 20130101; B60W 20/10 20130101;
B60Y 2200/12 20130101; B60L 58/15 20190201; B60W 2510/24 20130101;
Y02T 90/14 20130101; B60W 2710/24 20130101 |
Class at
Publication: |
320/134 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Claims
1. A method for charging a plurality of rechargeable battery
assemblies electrically connected in series with a battery charger,
each battery assembly comprising a rechargeable battery having a
positive terminal and a negative terminal, and means for
self-discharging the rechargeable battery electrically connected in
parallel with the battery terminals, said method comprising
continually determining a voltage across the positive and negative
terminals of each battery, then if the voltage is .gtoreq. a preset
value, self-discharge the battery until the voltage is equal to the
preset voltage, then further self-discharge the battery for a
period of time (t), wherein time (t) provides a discharge of the
battery charge corresponding to a preset percentage of the
battery's charge capacity.
2. A method for charging a plurality of rechargeable battery
parallel set assemblies electrically connected in series with a
battery charger, each battery parallel set assembly comprising a
plurality of rechargeable batteries, each having a positive
terminal and a negative terminal electrically connected in parallel
to form a battery parallel set, and means for self-discharging the
battery parallel set, said means being electrically connected in
parallel with said battery parallel set, said method comprising
continually determining a voltage across each battery parallel set,
then if the voltage is .gtoreq. a preset value, self-discharge the
battery parallel set until the voltage is equal to the preset
voltage, then further self-discharge the battery parallel set for a
period of time (t), wherein time (t) provides a discharge of the
battery parallel set charge corresponding to a preset percentage of
the battery parallel set's charge capacity.
3. A method for charging a plurality of rechargeable battery series
set assemblies electrically connected in series with a battery
charger, each battery series set assembly comprising a plurality of
rechargeable batteries, each having a positive terminal and a
negative terminal electrically connected in series to form a
battery series set, and means for self-discharging the battery
series set, said means being electrically connected in parallel
with said battery series set, said method comprising continually
determining a voltage across each battery series set, then if the
voltage is .gtoreq. a preset value, self-discharge the battery
series set until the voltage is equal to the preset voltage, then
further self-discharge the battery series set for a period of time
(t), wherein time (t) provides a discharge of the battery series
set charge corresponding to a preset percentage of the battery
series set's charge capacity.
4. A method for charging a plurality of rechargeable battery
parallel-series set assemblies electrically connected in series
with a battery charger, each battery parallel-series set assembly
comprising a plurality of rechargeable batteries, each having a
positive terminal and a negative terminal electrically connected in
parallel to form a battery parallel set, and a plurality of said
battery parallel sets electrically connected in series to form a
battery parallel-series set, and means for self-discharging the
battery parallel-series set, said means being electrically
connected in parallel with said battery parallel-series set, said
method comprising continually determining a voltage across each
battery parallel-series set, then if the voltage is .gtoreq. a
preset value, self-discharge the battery parallel-series set until
the voltage is equal to the preset voltage, then further
self-discharge the battery parallel-series set for a period of time
(t), wherein time (t) provides a discharge of the battery
parallel-series set charge corresponding to a preset percentage of
the battery parallel-series set's charge capacity.
5. A method for charging a plurality of rechargeable battery
series-parallel set assemblies electrically connected in series
with a battery charger, each battery series-parallel set assembly
comprising a plurality of rechargeable batteries, each having a
positive terminal and a negative terminal electrically connected in
series to form a series battery set, and a plurality of said series
battery sets electrically connected in parallel to form a battery
series-parallel set, and means for self-discharging the battery
series-parallel set, said means being electrically connected in
parallel with said battery series-parallel set, said method
comprising continually determining a voltage across each battery
series-parallel set assembly, then if the voltage is .gtoreq. a
preset value, self-discharge the battery series-parallel set until
the voltage is equal to the preset voltage, then further
self-discharge the battery series-parallel set for a period of time
(t), wherein time (t) provides a discharge of the battery
series-parallel set charge corresponding to a preset percentage of
the battery series-parallel set's charge capacity.
6. The method for charging of claim 1, 2, 3, 4 or 5, wherein the
preset percentage of the battery's capacity being further
discharged when voltage goes below the preset voltage is in the
range of 0.1% to 20%.
7. The method for charging of claim 1, 2, 3, 4 or 5, further
including providing at least one integrated circuit for controlling
the self-discharging of the batteries.
8. The method for charging of claim 7, wherein the at least one
integrated circuit performs functions of voltage detection and time
control for monitoring the conditions for self-discharging.
Description
[0001] This application is a continuation-in-part of pending U.S.
application Ser. No. 11/805,786, filed May 24, 2007, which claims
priority of U.S. Provisional Applications 60/923,747 and
60/930,646.
FIELD OF INVENTION
[0002] The present invention is concerned with rechargeable
batteries, and in particular with the recharging of rechargeable
batteries.
BACKGROUND OF THE INVENTION
[0003] 1. For batteries to be used for applications such as vehicle
starter, electric bikes, electric motorcycles, electric or hybrid
vehicles, etc, high voltage is essential owing to the increase of
efficiency and the decrease of cost. The increase of voltage
requires batteries to be connected in series. [0004] 2. Problems
associated with batteries in series are: [0005] a. when one battery
has a lower capacity, the capacity of the overall set of batteries
is dictated by the capacity of the battery of lower capacity;
[0006] b. if the battery possessing the lower capacity can not be
charged to full capacity during charging, the performance of the
entire battery set will be degraded owing to the lower capacity
battery. This is known in the art as cell imbalance; [0007] c. the
lower capacity of one specific battery can be caused by either high
self discharge or defects during battery production. [0008] 3.
Conventional ways to solve the cell imbalance problem are: [0009]
a. sorting the batteries in order to avoid inconsistency of the
batteries to be connected in series; [0010] b. charging the
batteries separately (e.g. U.S. Pat. No. 6,586,909), in order to
overcome the problems mentioned above, however, low voltage is
required for charging each battery to full (for example, the
lithium iron battery is charged to 3.65V) and this low voltage
charging is not energy efficient owing to conversions from normal
high voltage AC power source to low voltage DC power. Most prior
art systems and methods utilized in making the batteries balanced
during charging use complicated circuitry to detect and balance the
uncharged batteries (e.g. U.S. Pat. No. 7,068,011, U.S. Pat. No.
7,061,207, U.S. Pat. No. 6,882,129, U.S. Pat. No. 6,841,971, U.S.
Pat. No. 6,825,638, U.S. Pat. No. 6,801,014, U.S. Pat. No.
6,784,638, U.S. Pat. No. 6,777,908, U.S. Pat. No. 6,700,350, U.S.
Pat. No. 6,642,693, U.S. Pat. No. 6,586,909, U.S. Pat. No.
6,511,764, U.S. Pat. No. 6,271,645).
OBJECT OF THE INVENTION
[0011] It is an object of the present invention to provide a simple
device and method for charging a plurality of batteries
electrically connected in a series circuit.
SUMMARY OF THE INVENTION
[0012] The present invention is a rechargeable battery assembly,
having a rechargeable battery with a positive terminal and a
negative terminal, and means for self-discharging the rechargeable
battery when a voltage across the terminals is greater or equal to
a preset value. The means for self-discharging is electrically
connected in parallel with the battery terminals
DESCRIPTION OF THE DRAWINGS
[0013] The invention will become more readily apparent from the
following description thereof shown, by way of example only, in the
accompanying drawings, wherein:
[0014] FIGS. 1a-e are schematic illustrations of various
embodiments of battery assemblies of the invention;
[0015] FIG. 2a is a schematic illustration of a battery assembly of
the invention with an enlarged drawing of a self-discharging
circuit of the invention;
[0016] FIG. 2b is a schematic illustration the battery assembly of
the invention with an enlarged drawing of another embodiment of a
self-discharging circuit of the invention;
[0017] FIG. 3 is a schematic illustration of the battery assembly
of the invention having the self-discharging circuit disposed on a
case of the battery;
[0018] FIG. 4 is a schematic illustration of an electric power
supply system having battery assemblies of the invention;
[0019] FIGS. 5a-e are schematic illustrations of battery packs
having battery assemblies of the invention
[0020] FIGS. 6a-e are schematic illustrations of battery packs
having battery assemblies of the invention differing from those of
FIGS. 5a-e;
[0021] FIGS. 7a-e are schematic illustrations of battery packs
having battery assemblies of the invention differing from those of
FIGS. 5a-e and 6a-e;
[0022] FIGS. 8a-e are schematic illustrations of battery packs
having battery assemblies of the invention differing from those of
FIGS. 5a-e, 6a-e and 7a-e;
[0023] FIG. 9 is a schematic illustration of a battery pack
assembly having battery assemblies of the invention;
[0024] FIG. 10 is a schematic illustration of a battery system
having battery assemblies of the invention, as discussed in example
3;
[0025] FIG. 11 is a schematic illustration of a battery system
having battery assemblies of the invention, as discussed in example
5;
[0026] FIG. 12 is a schematic illustration of a battery system
having battery assemblies of the invention, as discussed in example
6; and
[0027] FIGS. 13(a)-(d) show experimental results for Example 6.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The present invention is especially important for resolving
the problems caused by batteries connected in series. A cell
imbalance problem during charging can be alleviated by creating a
device and methods that allows the leakage of current (energy) from
the batteries being overcharged. Instead of using very expensive
devices or ways to prevent overcharging, to achieve battery
equalization, as found in prior art devices and methods, the
present invention uses a method and device that reduces the current
being provided to a battery in the series circuit that is being
overcharged. Such method and device can be implemented for each
battery or battery set or battery pack being connected in series.
The terminology "battery set" used throughout the specification
means a plurality of batteries connected in parallel, or series, or
parallel-series, or series-parallel. The terminology "battery pack"
used throughout the specification means a plurality of battery sets
connected in parallel, or series, or parallel-series, or
series-parallel. The terminology "assembly" used throughout the
specification means a battery, a battery set, or a battery pack
accompanied with a means for self-discharge of the battery(s),
battery set or battery pack when the battery(s) is(are) being
overcharged
[0029] In the present invention a battery or batteries
self-discharge when overcharged. Since each battery, battery set,
or battery pack are provided with a "self-discharge" means, when
voltage reaches a preset parameter during charging, or even after
charging, a cell balance problem can be eliminated. This is the
core idea of the present invention.
[0030] FIG. 1(a) shows the structure of a "battery assembly". FIG.
1(b) shows the structure of a "parallel battery set assembly"; FIG.
1(c) shows the structure of a "series battery set assembly"; FIG.
1(d) shows the structure of a "parallel-series battery set
assembly"; and FIG. 1(e) shows the structure of a "series-parallel
battery set assembly". These assemblies are the basic units for use
in providing the battery pack. In these figures, as well as in the
remaining figures, an individual rechargeable battery is indicated
at 1, and a circuit for self-discharging the rechargeable
battery(s) is indicated at 3.
[0031] The present method of solving the cell imbalance problem is
shown in FIG. 2(a). As indicated in FIG. 2(a), each battery is
connected with a device 2 in parallel with the battery. Such device
is comprised of a switching element 6, a resistance element 7, a
voltage-detecting element 5a, and a switching element controller 5b
that opens or closes the switching element 6. The voltage-detecting
element detects the voltage of the battery and along with the
switching element controller controls the "opened" or "closed"
state of the switching element. The switching element, resistance
element, voltage-detecting element and switching element controller
can be disposed on a printed circuit board. However, since a
transistor can function as a combination of a voltage-detecting
element, controller, switching element, and a resistance element,
the device shown in FIG. 2(a) can be replaced by a transistor, or a
plurality of transistors connected in parallel (for adjusting the
resistance). Other possibilities are one transistor 8 connected
with a resistor 7 in series as shown in FIG. 2(b). In the case of
the transistor and resistor connected in series as indicated in
FIG. 2(b), the resistance of the resistor should be small in order
to minimize the voltage drop caused by the resistor thus affecting
the voltage detection of the transistor. The configuration of FIG.
2(b) can also be applicable to diodes such as LEDs, or a printed
circuit board consisting of the switching element and the
controller only.
[0032] When batteries are charged, if the voltage of one of the
batteries is above a preset upper limit, the switching element of
the device electrically connected in parallel to the battery
closes, therefore allowing current to flow through the resistor.
Thus, the charging current for the battery that passed the preset
upper limit voltage decreases, due to the presence of the device
connected in parallel to the battery. Such decrease is shown in
Example 1, below. Under such condition, other batteries are charged
in a normal current flow but the one that passed the upper voltage
limit has a decreased charging action. This is a basic mechanism of
the invention for the prevention of battery overcharging. It should
be mentioned that the resistance element can be any electronic
component that possesses a satisfactory resistance. For example, a
light bulb can be used as a source of resistance.
[0033] The elements of the device can be on a semiconductor chip 2,
which can be disposed anywhere close to the battery. FIG. 3 shows
one possibility of the semiconductor chip 2 being built-in on the
lid of a case of a battery. Also, for example, the chip can be
disposed between the cathode (the case) 11 and the anode (the
negative terminal) 12. Also, the chip can be placed inside the
battery case.
[0034] The resistor can be a variable one if further precise
control of the resistance is necessary. Details of the current
change for each battery during charging are further described
below:
EXAMPLE 1
Theoretical Demonstration of how Cell Equalization can be
Achieved
Assumptions:
[0035] 1. Four battery assemblies are connected in series as
indicated in FIG. 2(a). [0036] 2. Batteries (1), (3), (4) have
internal resistance of 5 mOhm, battery (2) has an internal
resistance of 10 mOhm. [0037] 3. Batteries (1), (3), (4) have open
circuit voltage of 3.3V, battery (2) has an open circuit voltage of
3.6V. [0038] 4. For each battery assembly, a resistor of 1.0 Ohm is
connected parallel to the battery. [0039] 5. A power supply of 15V
is applied to the four battery assemblies connected in series.
Calculation case 1 (when Paralleled Resistors are All Open): During
charging of the four battery assemblies, the voltage of each
battery can be represented as: [0040] Battery (1):
V.sub.1=Vo.sub.1+I.sub.1R.sub.1, V.sub.1 is the voltage of the
battery (1) during charging, Vo.sub.1 is the open circuit voltage
of battery (1), I.sub.1 is the current passing through battery (1)
and R.sub.1 is the internal resistance of the battery (1). [0041]
Battery (2): V.sub.2=Vo.sub.2+I.sub.2R.sub.2, [0042] Battery (3):
V.sub.3=Vo.sub.3+I.sub.3R.sub.3, [0043] Battery (4):
V.sub.4=Vo.sub.4+I.sub.4R.sub.4, Since no other resistors are
connected, I.sub.1=I.sub.2=I.sub.3=I.sub.4=I
15=(V.sub.1+V.sub.2+V.sub.3+V.sub.4)=(Vo.sub.1+Vo.sub.2+Vo.sub.3+Vo.sub.4-
)+I(R.sub.1+R.sub.2+R.sub.3+R.sub.4)
15-(Vo.sub.1+Vo.sub.2+Vo.sub.3+Vo.sub.4)=I(R.sub.1+R.sub.2+R.sub.3+R.sub.4-
)
15-3.3-3.6-3.3-3.3=I(0.005+0.01+0.005+0.005)
[0044] I=60 Amp--The current that passes through each battery
Calculation case 2, (when the Paralleled Resistor Circuit is Closed
for Battery (2)): Assume I' is the current passing through the
resistor and R' is the resistance of the resistor.
Then,
V.sub.2=I'R', I'=V.sub.2/R'
V.sub.2=Vo.sub.2+I.sub.2R.sub.2,
[0045] Considering the current balance:
(I'+I.sub.2)=I.sub.1=I.sub.3=I.sub.4=I
So,
V.sub.2=Vo.sub.2+(I-I')R.sub.2=Vo.sub.2+(I-V.sub.2/R')R.sub.2
[0046] Rearrange, then we get
V.sub.2=(Vo.sub.2+IR.sub.2)/(1+R.sub.2/R')
Thus,
[0047]
15=(V.sub.1+V.sub.2+V.sub.3+V.sub.4)=(Vo.sub.1+Vo.sub.3+Vo.sub.4)+I-
(R.sub.1+R.sub.3+R.sub.4)+(Vo.sub.2+IR.sub.2)/(1+R.sub.2/R')
So,
I=61.672 (A),
V.sub.2=(Vo.sub.2+IR.sub.2)/(1+R.sub.2/R')=4.175(V),
I'=V.sub.2/R'=4.175 (A),
I.sub.2=I-I'=57.497 (A)
[0048] If we substitute a resistor of 10 Ohm, then
I=60.168 (A),
V.sub.2=Vo.sub.2+(I-V.sub.2/R')R.sub.2=4.1975(V),
I'=V.sub.2/R'=0.4198 (A),
I.sub.2=I-I'=59.748 (A)
[0049] Conclusions from the Calculations: [0050] 1. With regards to
battery assembly of FIG. 2(a), when the switch of the resistor in
the parallel circuit is closed, current flows through the resistor,
and the charging current for battery (2) is decreased. [0051] 2.
While the switch of the paralleled resistor circuit is closed for
the battery assembly of FIG. 2(a), the charging current for other
batteries (1, 3, 4) is increased. [0052] 3. The resistance of the
resistor dictates the magnitude of the current decrease for battery
(2). The smaller the resistance, the bigger the magnitude of
current decrease. [0053] 4. Thus, the idea of incorporating a
resistor with each battery connected in series is effective in
balancing the capacity of all batteries by decreasing the charging
current of the battery that has a higher capacity, and by
increasing the charging current of the other batteries that have a
lower capacity. [0054] 5. It is clear that the resistor connected
in parallel with the battery should possess satisfactory cell
balancing function. Any electronic devices or components that
satisfy the function of voltage sensing and providing the source of
resistance are within the focus of the present invention.
EXAMPLE 2
Theoretical Calculation Demonstrating a Method of Charging a
Battery Assembly
Assumptions:
[0054] [0055] 1. Four battery assemblies are connected in series as
indicated in FIG. 2(a). [0056] 2. Batteries (1), (3), (4) have
internal resistance of 5 mOhm, battery (2) has an internal
resistance of 10 mOhm. [0057] 3. Batteries (1), (3), (4) have open
circuit voltage of 3.3V, battery (2) has an open circuit voltage of
3.6V. [0058] 4. Batteries (1), (2), (3), and (4) are subjected to a
constant current charge. The current is 2 A. [0059] 5. For
demonstration purpose, the battery being investigated, battery (2),
a resistor of 1.0 Ohm is connected parallel to the battery and the
circuit switch is closed.
Calculations:
[0060] Considering the current balance:
(I'+I.sub.2)=I.sub.1=I.sub.3=I.sub.4=I=2 (A)
V.sub.2=Vo.sub.2+(I-I')R.sub.2=Vo.sub.2+(I-V.sub.2/R')R.sub.2
[0061] Rearrange, then we get
V.sub.2=(Vo.sub.2+IR.sub.2)/(1+R.sub.2/R')
Substituting Vo.sub.2=3.6(V), I=2(A), R.sub.2 0.01 Ohm, R'=1
Ohm
We get:
V.sub.2=3.5842 (V)
I'=V.sub.2/R'=3.5842 (A),
I.sub.2=I-I'=2-3.5842=-1.5842 (A)<0
[0062] Conclusions from the Calculations: [0063] 1. The battery
that is overcharged will undergo discharging when the circuit
current (I) is less than the current that passes the resistor (I').
That is, (I-I'<0). [0064] 2. When batteries being overcharged
undergo discharge, cell balance can be achieved. [0065] 3. By
combining the calculation results shown in Example 1 and 2, it can
also be concluded that the cell balance charging method can be
implemented as either a constant voltage mode (but the charging
time required should be longer than the time required for the
condition of I<I'), or a constant current mode by passing a
current (I) that is less than the current that passes the resistor
(I'). [0066] 4. It can further be concluded that the charger can be
designed to have two modes for charging. One mode is the normal
constant current/constant voltage charge mode for a battery
system's normal use (end of charge executed by setting a certain
charging time). The other mode is the cell balance mode (constant
current charging) that can be used when a battery system possesses
less capacity than their normal use.
EXAMPLE 3
A Battery Pack and a Battery System
[0067] As mentioned above, a battery pack can be comprised of
battery sets, or battery set assemblies as shown in FIG. 1(a)-(e).
In the present invention, a battery pack may also connect with a
parallel circuit containing a switching element, a
voltage-detecting element, a controller, and a resistance element
to form a "battery pack assembly". The possible structures of
battery packs constructed using battery set assemblies are shown in
FIGS. 5(a)-(e), FIGS. 6(a)-(e), FIGS. 7(a)-(e), and FIGS. 8(a)-(e).
These figures represent the five unit structures shown in FIGS.
1(a)-(e) being connected in various circuit arrangements. In series
(FIGS. 5(a)-(e)), in parallel (FIGS. 6(a)-6(e)), in parallel-series
(FIGS. 7(a)-7(e)), and in series-parallel (FIGS. 8(a)-8(e)). Each
of the cases shown in FIGS. 5, 6, 7, and 8 can again be combined
with a parallel circuit containing the switching element, the
controller, the voltage-detecting element and the resistance
element to form a "battery pack assembly". An example of a "battery
pack assembly" is shown in FIG. 9
[0068] Similar to the case as a battery pack that is comprised of
battery sets or battery set assemblies, a battery system is
comprised of battery packs or battery pack assemblies. Again, the
possible structures of a battery system constructed using battery
pack assemblies can be in series, parallel, parallel-series, and
series-parallel. An example of a "battery system" is shown in FIG.
10.
[0069] One practical case is described here, that is an example of
the battery system for an electric motorcycle. Referring to FIG.
10, a typical electric motorcycle uses a battery system having 53V,
and 40 Ah. The battery system is comprised of four battery packs
(13.3V) connected in series. Each of the battery packs consists of
four lithium iron battery sets (3.33V) connected in series. And,
each of the battery sets consists of four 10 Ah batteries connected
in parallel. In this case, the best structure of the battery system
is the utilization of battery pack assemblies and the battery set
assemblies, as building blocks for the battery system. In such
arrangement, overcharging of battery packs and overcharging of
battery sets can be prevented. If the battery system is constructed
using battery pack assemblies but the pack assemblies are
constructed by battery sets only, some possible overcharging in the
battery set may occur after long time cycling. If the battery
system is constructed using battery packs only and the battery
packs are constructed using battery sets rather than battery set
assemblies, cell imbalance accompanied with overcharging during
charging can occur.
EXAMPLE 4
A Preferred Electric Power Supply System
[0070] An electric power supply system is the integration of
components including a charger 4, a battery system (packs or sets),
a control board 10, and a circuit breaker 9, as shown in FIG. 4.
Again, four battery assemblies of the invention are connected in
series as a simplest example for demonstration. Referring to FIG.
4, it can be seen that each battery is connected in parallel with a
circuit consisting of components as shown in FIG. 2(a) or FIG.
2(b). A control board is connected with electrical conductors to
each terminal of each of the batteries. Those electrical conductors
serve as a means for providing voltage detection. The other end of
the control board is connected to a circuit breaker. The charger is
connected directly to the two ends of the batteries electrically
connected in series. During a normal charging (constant
current/constant voltage), if any of the batteries exceeds a preset
overcharge voltage, the control board sends a signal to the circuit
breaker for charging termination. Similarly, during such
discharging, if any of the batteries is below the preset
termination voltage, the control board sends a signal to the
circuit breaker for discharging termination. These two actions
serve as battery protection to avoid overcharging and over
discharging. During normal charging, a preset time period is
allowed for the charging action (e.g. termination at 1.5 hours
after constant voltage charging). At that time, the batteries may
be more or less balanced. However, the batteries could be balanced
after several chargings, or by just starting a balance charging
(small current constant and current charge, current amplitude
I<I') mode, to allow constant current charging until all the
batteries are balanced.
[0071] In the present case, the control board can be a very simple
device for detecting the voltages of each battery connected in
series and sending signals to the circuit breaker for charging or
discharging action termination. The simplicity of the control board
is thus benefited by the characteristics of the batteries of the
invention since they possess current leakage during charging. In
the present invention, the shutting off of the charging is
preferably executed by a electromagnetic relay that turns off the
power input or output. This electromagnetic relay preferably
requires no power consumption during the idle state, and a pulse
signal generated by the control board determines the close and open
circuit status of the relay and therefore the on and off of the
battery charging.
EXAMPLE 5
Methods to Achieve Cell Equalization as Described in Example 1
[0072] Referring to FIG. 11, in the present example, a total of
eight 10 Ah lithium iron batteries are used for demonstrating the
charging method and the cell balancing characteristic of the
batteries during charging. Two cells are first connected in
parallel to form a parallel battery set. Each set of the batteries
are then connected with a circuit (a printed circuit board, for
example) electrically connected in parallel with the battery set to
form a battery assembly. Four battery assemblies are then connected
in series. In the present case, the first set, second set, third
set, and the fourth set are named for the four battery set
assemblies connected in series for clarity. All four set assemblies
are first charged to 100% full. The first battery set assembly is
then subjected to discharge 10% capacity (2 Ah). After this
procedure, all four battery set assemblies are connected in series
and this setup is referred to as the battery pack. A preset
self-discharge activation voltage is set at 3.75V in the present
case. The self-discharge circuit that is parallel to each battery
set has a resistance of 2 Ohm. After the above mentioned
procedures, the battery pack is subjected to a constant current
charge of 1.7 A. The voltage changes versus time for each set of
the batteries are shown in Table I. From Table I it can be seen
that the 2.sup.nd, 3.sup.rd, and 4.sup.th battery set assembly had
a voltage increase beyond 3.75V in the initial state. 5 minutes
after, the 2.sup.nd, 3.sup.rd, and 4.sup.th battery set assembly
came back to be stabilized at 3.75V. At this time, the current
passing through the resistor is measured to be 1.8 A.
[0073] The 1.sup.st set of the battery set assembly increases its
voltage gradually to 3.75V after 80 minutes and this is the end of
the charge balance action. In the present experiment, I (power
supply current) is set to be less than I' (current passing
resistor). As a result, the voltages for the 2.sup.nd, 3.sup.rd,
and 4.sup.th sets of battery set assemblies were stabilized at
3.75V during charging. Full balances of the four sets of battery
set assemblies were achieved after a certain period of time. It was
observed that if current I is set to be slightly larger than
current I' (1.8 A in this case), and the voltages of the 2.sup.nd,
3.sup.rd, and 4.sup.th battery sets could be higher than 3.75V
during the constant current charge. However, if the constant
voltage charge is set at 15V as the second step charging, a voltage
decrease of 2.sup.nd, 3.sup.rd, and 4.sup.th battery sets can be
observed (when current I starts decreasing below current I') and
the four sets of battery set assemblies can be balanced eventually,
but requiring a longer time.
[0074] In addition to the self-discharge setup and mechanism
described above, there is another feature that can be integrated to
the self-discharge setup as shown in FIGS. 2 (a) and 2(b) by adding
a timer (time counter) or a charge counter that controls the amount
of charge being self-discharged under certain conditions. The core
idea of adding a timer or a charge counter is to resolve the
problem of batteries, battery sets, or battery packs, being
connected in series, that can not be charged with prolonged
constant voltage charge, that is, when a charger or any means of
charging (e.g. solar or wind turbine charging) do not provide long
and steady constant voltage charging. In order to make batteries
connected in series be balanced, without the presence of prolonged
constant voltage charge, the self-discharge setup is provided with
a timer. The function of the timer is to set a certain amount of
charge in a battery to be self-discharged when certain conditions
exist. While batteries are overcharged to a preset voltage V', the
self-discharge mechanism is triggered. The self-discharge action
continues until the battery voltage goes below the preset voltage
V' and then the timer is triggered for further self-discharge for a
certain period of time (e.g. 2% of the battery capacity, that is
the time required to discharge the battery 2% of it's capacity).
Although 2% is given as a preferred amount, a discharge amount of
between about 2% and 20% of the battery's capacity is possible in
practice of the invention. The advantages of this method include
the following: (1) This time delayed self-discharge setup offers
the functions described earlier in regard to Example 5, above, that
is, when any of the battery set assemblies being connected in
series is subjected to self-discharge when the voltage exceeds the
preset voltage V', all the battery set assemblies being connected
in series will be balanced eventually after prolonged constant
voltage charge; (2) Unstable charging conditions, such as renewable
energy power source charging (e.g. Solar panels, or wind turbines .
. . etc.), or any other type of chargers that do not offer
prolonged constant voltage charging will still be useful for
charging the batteries while maintaining the performance (function)
of battery cell balance. This can be realized using the same
battery set assemblies described in Example 5 above, as an example,
that is charged to a certain voltage and a cut-off is performed
without constant voltage charging. The battery set assemblies being
connected in series that have already exceeded the preset voltage
limit V' will be kept discharging and a further self-discharge will
be performed even when the battery voltage drops down below the
preset voltage V'. Owing to an additional self-discharge performed
to those battery set assemblies already exceeding the preset
voltage V', the capacity difference between those exceeding V'
before cut-off (with self-discharge triggered) and those below V'
before cut-off (without self-discharge being triggered) will be
closer in capacity if the time utilized for constant voltage charge
is insufficient; and (3) The constant voltage charging can be
replaced by several voltage cut-off charging methods, as will be
discussed in more detail in Example 6, below.
EXAMPLE 6
Method to Achieve Battery Cell Equalization without Prolonged
Constant Voltage Charging
[0075] The purpose of the present example is to demonstrate the
need for the time delayed function of the invention for the
self-discharge setup that achieves a battery cell balance condition
without having a prolonged time for constant voltage charging.
[0076] Referring to FIG. 12, in the present example a total of four
10 Ah lithium iron batteries are used for demonstrating the
charging method and the cell balancing characteristic of the
batteries during charging. Each battery 1 is connected with a
circuit 2 electrically connected in parallel with the battery to
form a battery assembly 3. Each circuit 2 contains a voltage
detector 5a, a 10 Ohm resistor 7, and a timer 13, that allows
self-discharge of the battery when the battery voltage exceeds or
is equal to 3.65V, followed by a further self-discharge for a time
period of 15 minutes when the battery voltage goes below 3.65V.
Four battery assemblies are connected in series. In the present
example the 4 battery assemblies in FIG. 12 have batteries numbered
(1), (2), (3), and (4). The voltage changes versus time for each
battery assembly are shown from FIGS. 13(a) to 13(d). The current
versus time for the battery pack, which contains the four battery
assemblies in series, is shown in FIG. 13(e). All four battery
assemblies are first charged to 100% of capacity and balanced
initially (3.65V.+-.0.03V), as can be seen from FIGS. 13(a) to
13(d). The first battery assembly (battery (1)) is then subjected
to discharge 6.6% capacity (0.66 Ah) using a 5 Ohm resistor for one
hour. After this procedure, the battery pack that contains the four
battery assemblies connected in series is subjected to a constant
voltage charge set at 14.7V. However, the charger is set to cut-off
when any of the battery assembly is charged above 3.70V. It can be
seen from FIG. 13(a) to 13(d) that the 2.sup.nd, 3.sup.rd, and the
4.sup.th battery assemblies (batteries (2), (3), and (4)) increases
rapidly in voltage as soon as the charger starts charging. The
charger stops charging almost immediately after it is activated.
However, since the 2.sup.nd, 3.sup.rd, and the 4.sup.th battery
assemblies triggered the self-discharge voltage preset at 3.65V, a
continuous drop in voltage is observed for each of them, even after
the cut-off of the charger. In comparison to the 2.sup.nd,
3.sup.rd, and the 4.sup.th battery assemblies, the 1.sup.st battery
assembly does not have any self-discharge after the cut-off of the
charger thus a flatter voltage profile is observed. After 8 cycles
of charging it is observed that the 1.sup.st battery assembly
becomes the only one that performs self-discharge (increase over
3.65V in voltage) and cut-off of the charging process when it
exceeds 3.70V. This result suggests cell balance can be achieved
with multiple charging by setting voltage as a cut-off. A recovery
of 6.6% battery capacity difference can be compensated for with
multiple charging steps with the utilization of the time delayed
self-discharge setup for each of the batteries. With a further
charging of the four batteries in series at 14.7V with the removal
of self-discharge setup on each battery, an overall capacity input
of 3.7% to 0 current is obtained. This implies that all the
batteries are close to being fully charged after 8 consecutive
chargings, even without the presence of prolonged constant voltage
charging. According to the experimental results shown, there is no
rigid limitation of what components are used for the time-delayed
self-discharge mechanism. Any integrated circuits, transistors, or
even setups integrating components including voltage sensor,
resistor, and timer or charge counter manually can achieve the goal
of balancing the batteries connected in series without prolonged
constant voltage charging.
[0077] Although Example 6 is for four battery assemblies connected
in series as shown in FIG. 12, the method of the invention applies
to batteries arranged as shown in FIGS. 5(a)-11, and expanded
versions of those arrangements.
TABLE-US-00001 TABLE I Voltage versus time for each set of the
batteries. 40138 12V20Ah Lithium Iron Cell Balance Charging Test
Constant current charge (current = 1.7 A) Set Number 1 2 3 4
Initial Voltage (V) 3.344 3.354 3.348 3.35 Time (minutes) Voltage
for each set (V) 0 3.401 3.883 3.852 3.861 5 3.457 3.761 3.757
3.759 10 3.462 3.752 3.761 3.762 15 3.473 3.753 3.755 3.757 20
3.481 3.756 3.751 3.754 30 3.499 3.759 3.752 3.757 40 3.558 3.753
3.756 3.755 50 3.633 3.758 3.754 3.756 60 3.757 3.751 3.753 3.754
70 3.752 3.757 3.756 3.752 80 3.759 3.751 3.754 3.755
* * * * *